This invention relates generally to a retorting type apparatus, process and system for aboveground recovery of oil from oil shale and more particularly to an anaerobic retorting apparatus, process and system for separating, vaporizing and recovering oil and gas from crushed oil shale.
Many aboveground retorting processes are known in the prior art. Only a few of these retorting apparatus, processes and systems however have been constructed and studied for the purpose of developing an apparatus and system suitable for handling the recovery of oil from the large quantities of oil shale material that must be handled to meet the modern requirements for an efficient workable, and feasible system.
Those skilled in the art will recognize that a technically and economically feasible retorting apparatus, process and system must be capable of thermally degrading the solid organic material (kerogen) in the shale. Thus, such retorting apparatus, processes and systems must be capable of heating the oil shale to 800.degree.-1100.degree. F. (425.degree.-600.degree. C.), to decompose the kerogen into the oil and gaseous components so that these components can be separated and recovered from the base material of the shale.
Various types of apparatus and systems for aboveground retorting processes for removing oil and gas from oil shale have been designed, developed and tested in the United States. These are generally identified as the Gas Retorting System, and the Tosco II Retorting System. The apparatus and system for these prior art processes and the respective pros and cons thereof are outlined in depth at Chapter 9 entitled Retorting Technology of Oil Shale by Gerald U. Dinneen in the publication, Developments in Petroleum Science, 5; Oil Shale edited by T. F. Yen and G. V. Chilingarian published in 1976 by American Elsevier Scientific Publishing Company, New York, N.Y. 10017.
In Brazil, Petrobras, a Brazilian Government Corporation has developed an aboveground retorting process identified as the Petrosix process. In this Petrosix process a vertical retort tower is charged with ground oil shale which is moved by gravity from the top to the bottom thereof through heating, retorting, and cooling zones, in which a recycled gas stream entering at the bottom of the vertical retort tower recovers heat as it moves upwardly in a counter-flow direction to the downwardly moving oil shale until it reaches an intermediate or medial section of the vertical retort tower where it combines with heated retort gas for providing the necessary heat to raise the temperature of the downwardly moving oil shale to the required decomposition temperatures for separating and vaporizing oil and gas from the oil shale. The entire mixture of recycled and heated gases, separated and vaporized oil, all move upwardly in counter-flow to the entering oil shale and pass from a suitable outlet or discharge port at the upper end of the vertical retort tower. The mixture is then passed to means for separating the product oil and product gas. A portion of the product gas is recycled for reuse in the vertical retort tower. This process is characterized by the use of an external heat source and by direct heat exchange between the solid oil shale and the upflowing gaseous heat exchange medium which is used to establish the temperature required for decomposition of the organic matter in the downwardly moving oil shale in the vertical retort tower. The following U.S. patents were cited in related U.S. patent application Ser. No. 508,738, filed June 29, 1983, which, in turn, is a divisional application of the aforementioned U.S. patent application Ser. No. 457,975: U.S. Pat. No. 2,448,223 to Lantz; U.S. Pat. No. 2,581,041 to Ogorzaly et al; U.S. Pat. No. 2,698,283 to Dalin, U.S. Pat. No. 2,710,828 to Scott, Jr.; U.S. Pat. No. 3,384,569 to Peet; U.S. Pat. No. 3,377,266 to Salnikov; and U.S. Pat. No. 4,056,461 to Unverferth. The relevance of these references is discussed in the aforementioned U.S. patent application Ser. No. 508,738.
A problem that may result in prior art system due to improper pressure differentials is that the vaporized kerogen and components thereof may condense in the tower before being drawn off. This, of course, causes problems in the flow of material through the tower and may even be dangerous.
The present invention provides an improved retorting process in which an elongated tower defines a passage means for passing by gravitational movement crushed oil shale fragments generally in a size range not in excess of 3/4", through drying, preheating, cracking and distillation, and waste heat recovery zones formed in the elongated tower. These zones are established and characterized by indirect heat exchange means. The waste heat from the waste heat recovery zone is recovered and passed to both the cracking and distillation zone and preheat recovery zone. A separate externally heated gas stream or heat transfer fluid provides the heat exchange medium for the heating of the oil shale during its gravitational movement through the cracking and distillation zone. In the cracking and distillation zone, the preheated oil shale is raised to the required temperature for the decomposition of the kerogen organic matter. In the decomposed state the kerogen is vaporized and the hydrocarbon and gaseous components of the kerogen are, in the vapor state, readily separated from the gravitational moving crushed oil shale in the elongated housing or recovery tower. This separation process is controlled by maintaining atmospheric pressure in the elongated housing or recovery tower at two locations. Location No. 1 may be in the drying zone or the preheat zone. This will permit water vapor to exit from the top of the elongated housing or recovery tower. Location No. 2 is a predetermined distance from the discharge outlet for spent oil shale. By maintaining the pressure conditions in the elongated housing or recovery tower at atmospheric pressure, the decomposed kerogen vapors can be drawn off or will exit under pressure automatically from the cracking or distillation zone.
By this means the cracking and distillation zone will be at a pressure above atmospheric pressure and will operate in an ambient atmosphere substantially lacking in oxygen.